自定义 JTableHeader 导致 NullPointerException

Custom JTableHeader causes NullPointerException

我一直在尝试使用 Oracle's How To Use Tables to create a JTable with tool tips for each column header. The demo 中的代码似乎可以工作,但是无论我是直接粘贴代码还是抽象我自己的代码 class,我都会收到 NullPointerException SynthTableHeaderUI.java 行 233 中调用 getTableCellRendererComponent()。这是由于调用 header.getTable() which returns null on any table 我尝试 setTableHeader() on,即使我setTableHeader(new JTableHeader(tblWhatever.getColumnModel()));

我从演示中粘贴的函数位于自定义 TableModel 中,否则效果很好,如下所示:

public class TestTableModel extends AbstractTableModel {
private final String[] columnNames = {"Name", "Height", "Weight", "Age"};
private final String[] columnToolTips = {"Person's Name",
                                     "Height in centimetres.",
                                     "Weight in kilograms.",
                                     "Age in years as of 2015-Jan-01."};
private ToolTipTableHeader ClientTableHeader; // = new ToolTipTableHeader((new JTable()).getColumnModel(), columnToolTips);

    private final Client[] List = {
        new Client("Abigale", 150, 108, 22),
        new Client("Bob", 180, 175, 36),
        new Client("Charles", 150, 210, 52)
    };

    /*
     * Constructors
     */
    public TestTableModel() {
        super();
    }

    public void setTableHeader(JTable tblClients) {
        tblClients.setTableHeader(createDefaultTableHeader(tblClients.getColumnModel()));
    }

    /*
     * AbstractCellEditor Implementations
     */
    @Override
    public Class getColumnClass(int col) throws java.lang.IndexOutOfBoundsException {
        switch(col) {
            case 0: return String.class;  //.ClientName;
            case 1: return Integer.class; //.Height;
            case 2: return Integer.class; //.Weight;
            case 3: return Integer.class; //.Age;
            default: throw new IndexOutOfBoundsException("Column " + col + ": class not accounted for in " + this.getClass().getName() + ".getColumnClass");
        }
    }

    @Override
    public int getColumnCount() { return columnNames.length; }

    @Override
    public String getColumnName(int col) { return columnNames[col]; }

    @Override
    public int getRowCount() { return List.length; }

    @Override
    public Object getValueAt(int row, int col) throws java.lang.IndexOutOfBoundsException {
        switch(col) {
            case 0: return List[row].ClientName;
            case 1: return List[row].Height;
            case 2: return List[row].Weight;
            case 3: return List[row].Age;
            default: throw new IndexOutOfBoundsException("Column " + col + ": value not accounted for in " + this.getClass().getName() + ".getValueAt");
        }
    }

    @Override
    public boolean isCellEditable(int row, int col) { return true; }

    @Override
    public void setValueAt(Object value, int row, int col) {
        switch(col) {
            case 0: List[row].ClientName = (String) value; break;
            case 1: List[row].Height = (Integer) value; break;
            case 2: List[row].Weight = (Integer) value; break;
            case 3: List[row].Age = (Integer) value; break;
            default: throw new IndexOutOfBoundsException("Column " + col + ": value not accounted for in " + this.getClass().getName() + ".setValueAt");
        }
        fireTableCellUpdated(row, col);
    }

    /*
     * Extensions
     */

    //Implement table header tool tips.
    protected JTableHeader createDefaultTableHeader(TableColumnModel tcmThis) {
        return new JTableHeader(tcmThis) {
            @Override
            public String getToolTipText(MouseEvent e) {
                String tip = null;
                java.awt.Point p = e.getPoint();
                int index = columnModel.getColumnIndexAtX(p.x);
                int realIndex = 
                        columnModel.getColumn(index).getModelIndex();
                return columnToolTips[realIndex];
            }
        };
    }
}

自定义 class 看起来像这样:

public class ToolTipTableHeader extends JTableHeader {
    private final String ColumnToolTips[];

    ToolTipTableHeader(TableColumnModel cm, String iniToolTips[]) {
        super(cm);

        if(iniToolTips.length != cm.getColumnCount()) 
            throw new InvalidParameterException("The size of iniToolTips must be precisely equal to the columnModel column count.");
        ColumnToolTips = iniToolTips;
    }

    @Override
    public String getToolTipText(MouseEvent meToolTipEvent) {
        String tip = null;
        if(columnModel == null) return "columnModel == null";
        if(meToolTipEvent == null) return "meMouseEvent == null";
        Point p = meToolTipEvent.getPoint();
        int index = columnModel.getColumnIndexAtX(p.x);
        int realIndex = columnModel.getColumn(index).getModelIndex();
        return ColumnToolTips[realIndex];
    }
}

初始化在 JDialog 构造函数中完成(JTable tblTest 在设计器中创建):

public TestForm(java.awt.Frame parent, boolean modal) {
    super(parent, modal);
    initComponents();

    TestTableModel htmTest = new TestTableModel();
    tblTest.setModel(new TestTableModel());
    htmTest.setTableHeader(tblTest);
}

我注意到默认 JTableHeader 的构造函数不需要将 JTable 传递给它,我已经实现了构造函数和覆盖的 getTable() t 似乎被称为。当我写这篇文章时,我意识到有效的演示将函数放在自定义 JTable 中,我不想这样做,因为我使用的是 NetBeans IDE 并且我不知道向设计器添加自定义 table 的简单方法。

我错过了什么?如何在不创建自定义 JTable 的情况下实现它?感谢您的指点。

JTableHeader 扩展 必须 添加为 JTable 构造的一部分。 table header 的任何后续设置都会导致上述错误。如果使用 NetBeans,请转到 Design Mode 以获取 dialog/form/panel、select 和 table,然后单击 Code 选项卡 属性 window。添加(例如)

new javax.swing.JTable() {
    //Implement table header tool tips.
    protected JTableHeader createDefaultTableHeader() {
        return new JTableHeader(columnModel) {
            public String getToolTipText(MouseEvent e) {
                String tip = null;
                java.awt.Point p = e.getPoint();
                int index = columnModel.getColumnIndexAtX(p.x);
                int realIndex =  columnModel.getColumn(index).getModelIndex();
                return myToolTips[realIndex];
            }
        };
    }
};

自定义创建代码字段并确保定义

private final String[] myToolTips = {
    "Column 0 tool tip",
    "Column 1 tool tip",
    // ...
    "Final column tool tip"
};

在 dialog/form/panel 的 class 的某处。这可行,但仍然有点不雅,因为它需要为使用该 table 模型的每种形式完成,而不是能够将其融合并拥有一个 class 来设置 table.